Various technologies for diagnosing an abnormality inside a rotating machine (for example, a compressor, a motor, or a power generator) have been proposed. For example, there has been proposed a diagnosing method for a compressor of non-contact type in which an AE wave generated by a contact between a male rotor and a female rotor of the rotating machine during rotation of the rotors and rotational signals of the rotors are detected simultaneously to thereby perform diagnosis about a contact between the rotors on the basis of the detected AE signal and rotational signals, the method being characterized by amplifying and demodulating the AE signal, performing a frequency analysis and arithmetic mean processing to the output, and comparing the result with a determination reference on the basis of the rotational signals to perform diagnosis about a contact between the rotors or the like (for example, see Patent Literature 1).
Also, there has been proposed an irregular contact detecting method for detecting an irregular contact state in a rotating machine which includes a first rotor and a second rotor rotating in a pair, the method being characterized by demodulating an elastic wave signal output from the rotating machine, and determining that the rotors are in contact with each other if the demodulated elastic wave signal includes at least one of a rotational frequency component of the first rotor and a rotational frequency component of the second rotor at a predetermined level, determining that a rotor is in contact with the casing if the demodulated wave signal contains a frequency component obtained by multiplying the number of blades of the first rotor and the rotational frequency of the rotor, and a frequency component obtained by multiplying the number of blades of the second rotor and the rotational frequency of the rotor, and determining that a rotor is in contact with a sealing member if a wave level of the elastic wave signal output from the rotating machine is larger than a predetermined level, but the mutual contact between the rotors and the contact between a rotor and the casing are not determined (see, Patent Literature 2).
Further, there has been proposed an abnormality diagnosing apparatus in which an oscillation of a rotating machine is detected and then applied with a continuous wavelet transform, the transformed signal is added in a frequency axis direction, and a is determined based on the result of the addition (for example, see Patent Literature 3).